The hydraulic fracture test was developed under the Strategic Highway Research Program to address the need for a more rapid, less expensive test for concrete aggregate freeze-thaw durability. Although the test concept appeared sound, the original test and analysis procedures were not sufficiently reliable and accurate to merit widespread adoption and implementation. Several follow-up research efforts have been performed, and each has resulted in improvements to the test. The results of the most recent study, which evaluated changes in both the test procedure (to include additional test sieves for better characterization of particle fractures) and the analysis procedures, are described. The "hydraulic fracture index" has been replaced by a model that predicts freeze-thaw test dilation as a function of the distribution of particle mass retained on the test sieves. This model was developed using data obtained from freeze-thaw and hydraulic fracture testing of 18 quarried carbonate and gravel aggregate sources; the resulting correlation is exceptional (r-squared = 0.98). An additional improvement is the development of a large test chamber capable of handling aggregate samples five times larger than the original small chamber, which thereby allows aggregate durability characterization with a single test run. It is believed that the hydraulic fracture test is now ready for more broad-based validation testing and eventual widespread acceptance and implementation as an accurate screening tool for concrete aggregate freeze-thaw durability.
Abstract